Shearwater and aqualung i300

[Scuba Bobby]

Heya,

I have both a Shearwater petral 2 and a aqualung i300c.
The petral is my main and the i300c is my backup

The petral 2 is set to 40/85 GF

I did a dive recently to 40m with both, my shearwater put me into deco (only 2 min)
However my I300c still gave me 2min before I hit my NDL.
Both where set to the same gasses safety stops ect.

Why would this be? And how can I set my petral 2 to match the GF of the i300c?
The reason I'd like to do this is more of a safety issue, if I need to switch computers because the petral 2 stops working I'd like to know that they are essentially making me do the same stops ect.

Thanks in advance

 

[Scuba_Oscar]

Hey Bobby,

I did some research on the algorithms that the 2 dive computers you mentioned use. The Petral 2 uses the Buhlmann ZHL-16c. The i300c uses a modified version of the Buhlmann ZHL-16c, which may be causing your discrepancy. Additionally, both computers have Conservative Factor (CF) settings. Having this set to “on” will make your dive profile more conservative. You could try turning it off if it’s defaulted to on and seeing if your dive profiles match after that change.

 

[GreggS]

I have a Peregrine TX with an Oceanic OCi as a backup. I have the OCi set on the PZ+ algorithm, which is what the i300 runs. I set my Peregrine at 45/90 and the 2 computers are pretty much dead on. But there is nothing wrong with the settings you have. If either of your computers is to be more liberal, it should be your backup.

 

[rongoodman]

But there is nothing wrong with the settings you have. If either of your computers is to be more liberal, it should be your backup.

Especially if your backup is going to lock you out if you make it unhappy, which the Aqualung will do.

 

[GreggS]

Especially if your backup is going to lock you out if you make it unhappy, which the Aqualung will do.

Exactly right.

 

[Scuba Bobby]

I have a Peregrine TX with an Oceanic OCi as a backup. I have the OCi set on the PZ+ algorithm, which is what the i300 runs. I set my Peregrine at 45/90 and the 2 computers are pretty much dead on. But there is nothing wrong with the settings you have. If either of your computers is to be more liberal, it should be your backup.

Interesting, I may try changing the GF to 45/90 and see if that brings them more in line. I want to keep the i300c as my back up for obvious reasons.

 

[GreggS]

Well, just remember, 2 minutes at 80-100 ft is not a lot of difference. You can have more dive time at shallower depths. The best practice is to not flirt with your NDL by running it down to 0. Always start ascending before you run out of time. Your computers algorithm is only an estimate of what is actually happening inside your body. There have been plenty of divers to get bent without there computers going into deco. But that being said, always pay attention to what you're computer is telling you and dive accordingly by not pushing the limits. We want you to be safe.

 

[Scuba Bobby]

Well, just remember, 2 minutes at 80-100 ft is not a lot of difference. You can have more dive time at shallower depths. The best practice is to not flirt with your NDL by running it down to 0. Always start ascending before you run out of time. Your computers algorithm is only an estimate of what is actually happening inside your body. There have been plenty of divers to get bent without there computers going into deco. But that being said, always pay attention to what you're computer is telling you and dive accordingly by not pushing the limits. We want you to be safe.

100% I don't like going into deco unless I'm doing ADP with a deco stage, I was more curious at the time difference between them, and that my i300c as a back up was more liberal. I have adjusted to 40/90 (as stated above) to see if that brings them more in line.

My thinking behind this is if I have to switch to my back up it will give the safety stops needed (even though I would add extra to be safe) but also wouldn't get locked out if that makes sense.

 

[scubadada]

...I have adjusted to 40/90 (as stated above) to see if that brings them more in line...

Hi @Scuba Bobby

Another thing to keep in mind is that the 2 computers may run differently on a first clean dive vs. a repetitive dive. You may want to watch your computers.

As an example, I run a Shearwater Teric at a GF high of 95 and an Oceanic VT3 running DSAT. On the first, clean dive, the VT3 has a longer NDL, especially when deeper. On a repetitive dive, the Teric generally has a longer NDL, especially if shallower. It is not possible for me to have my computers match perfectly. For NDL dives, the more conservative of the 2 controls the dive. For light deco, I clear one or both of the computers.

I use SurfGF at the safety stop or the deco stop to adjust my surfacing GF to the desired value. I'm not sure if your Petrel 2 has SurfGF

 

[Scuba Bobby]

Hi @Scuba Bobby

Another thing to keep in mind is that the 2 computers may run differently on a first clean dive vs. a repetitive dive. You may want to watch your computers.

As an example, I run a Shearwater Teric at a GF high of 95 and an Oceanic VT3 running DSAT. On the first, clean dive, the VT3 has a longer NDL, especially when deeper. On a repetitive dive, the Teric generally has a longer NDL, especially if shallower. It is not possible for me to have my computers match perfectly. For NDL dives, the more conservative of the 2 controls the dive. For light deco, I clear one or both of the computers.

I use SurfGF at the safety stop or the deco stop to adjust my surfacing GF to the desired value. I'm not sure if your Petrel 2 has SurfGF

That's interesting.

Thank you, I have just had my petral refurbished, so I'll see if that affects it at all when I next dive. At the moment I have a GF at 45/90.